This letter describes a procedure based on the radiative transfer theory to calibrate the scattering contributions from the Generalized Freeman-Durden (GFD) polarimetric decomposition over corn fields. The Tor Vergata electromagnetic model (TOV) is used to simulate canonical scattering mechanisms that are compared with those obtained applying GFD to both simulated and L-band SAOCOM-1A data. The proposed method first analyzes the error between the model and the GFD applied to the simulated data. A multivariate data fitting is then performed to derive a new expression of the GFD powers, which is tested on L-band real data. The GFD volume power obtains the greatest benefit from the calibration, reducing the Root Mean Square Error (RMSE) with respect to the corresponding TOV model contribution to 0.006 in linear units. To further test the procedure, a linear regression model is used to estimate soil moisture using the calibrated GFD powers from SAOCOM-1A real data. The retrieval performance, evaluated through a Leave-One-Out (LOO) cross-validation against in situ data, shows a significant improvement: the calibrated GFD powers leads to an increased linear correlation (0.32 to 0.57), while the RMSE is reduced (0.096 to 0.055 m³/m³).

The NASA ISRO Synthetic Aperture Radar (NISAR) is scheduled for launch early in 2024 from the Satish Dhawan Space Centre (SDSC), at Sriharikota, near Chennai, India. This mission is the result of a collaboration between NASA and Indian Space Research Organization (ISRO), where NASA has contributed elements of the mission such as an L-band SAR, and ISRO has contributed other elements, such as an S-band SAR. After successful launch, the NISAR mission will collect left-looking L-band SAR data over most of the Earth’s land areas twice during every 12-day exact repeat orbit. (once while in an ascending orbit direction and once while in a descending orbit direction). NASA and ISRO have individual and joint requirements on the mission that include the performance of the imaging radars onboard the spacecraft. For example, NASA must demonstrate that this L-band SAR will achieve a set of identified science measurement accuracy requirements that span Ecosystem science, Solid Earth science, and Cryosphere science disciplines. Likewise, ISRO has several applications objectives on both the L-band and S-band data from NISAR that the ISRO science team and project will be developing and testing. Pre-launch and post-launch activities have been planned to validate that these requirements are met. Here, we will discuss how the NASA plans are being executed and will present any initial results at the conference.

In this paper, the results obtained by applying two polarimetric SAR decompositions to a time-series of L-band radar data, in terms of scattering contributions, are compared with the simulations of the Tor Vergata electromagnetic model. The objective was to evaluate the capability of polarimetric SAR decompositions to single out those scattering mechanisms mostly correlated to soil moisture or vegetation. We performed the analysis by using L-band full-polarimetric SAOCOM-1A data acquired over an agricultural region in the Monte Buey site (Córdoba Province, Argentina) and by considering five corn fields.

In this paper, a joint analysis of multi-frequency SAR data has been performed to assess their sensitivity to soil moisture variations over an agricultural area. The main objective was evaluating the performances offered by C and L bands in terms of sensitivity to soil moisture. We used L-band quad-polarimetric data acquired by SAOCOM-1A and C-band dual-polarimetric data collected by Sentinel-1A over an agricultural area located in the Córdoba Province, Argentina. We analyzed the temporal evolution of the backscattering coefficient at different polarizations with respect to in-situ soil moisture measurements collected during a field campaign conducted by the Argentinian Space Agency as well as data recorded by a permanent network of ground stations. Sensitivity to other variables, such as the NDVI, is also discussed and analyzed.

In this work, the sensitivity to soil moisture of different scattering mechanisms observed by an airborne polarimetric radar operating at L-band has been investigated. The main objective was assessing the capability of a fully polarimetric radar system to disentangle the change in soil moisture under different vegetation covers. We used polarimetric data collected by the NASA UA VSAR airborne radar flying over the Yucatan Lake site in Louisiana. Six overflights were analysed, and six regions of interest characterized by different vegetation covers were selected. The temporal trends of the magnitude of different scattering mechanisms, according to the Freeman-Durden and the Nonnegative Eigenvalue decompositions, as well as of the NDVI and a nearby precipitation gauge are analysed and discussed with reference to the theoretical expectations.